The invention discloses a desulphurization synergist for a wet-method smoke desulphurization system used for a fire plant. The desulphurization synergist consists of the following ingredients: an interface active agent, a cosolvent, a pH buffer agent and an oxidation catalyst, wherein the preferable weight percent of each ingredient is as follows: 40 to 60 percent of interface active agent, 20 to 40 percent of cosolvent, 5 to 15 percent of pH buffer agent and 2 to 5 percent of oxidized catalyst. The desulphurization synergist is added into a calcium absorption agent, and the application concentration is 150mg/L to 600mg/L. By adopting the desulphurization synergist, the solubility equilibrium of calcium absorption agent can be promoted to move towards a positive direction, and the solubility of the calcium can be improved; the pH of a gas-liquid interface is stabilized, and the dissolving speed of sulfur dioxide is increased; the oxidation speed is increased, and the generation of gypsum is accelerated; the circulation amount of absorption slurry is reduced, the consumption of the absorption slurry is reduced, an energy-saving and consumption-reducing purpose is achieved, the cost is reduced, and benefit increasing can be achieved.